Method of producing an electronic device

ABSTRACT

An electronic device having an element body, wherein dielectric layers and internal electrode layers are alternately stacked, wherein a hetero phase is formed in the dielectric layers and/or the internal electrode layers; and the hetero phase includes a Mg element and a Mn element. Preferably, the hetero phase is formed at least at a part near boundaries of the dielectric layers and the internal electrode layers.

This is a Divisional of application Ser. No. 11/212,885 filed Aug. 29,2005, now issued as U.S. Pat. No. 7,295,422. The disclosure of the priorapplication is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic device, such as amultilayer ceramic capacitor, and the production method, andparticularly relates to an electronic device having low IR temperaturedependency and a reliable average lifetime, etc. and the productionmethod.

2. Description of the Related Art

A multilayer ceramic capacitor as an electronic device is widely used asa highly reliable compact electronic device having a large capacity, andthe number to be used in an electric apparatus is also large. In recentyears, as apparatuses becoming more compact with higher performance,demands for a multilayer ceramic capacitor to be more compact, larger incapacity, lower in price, and higher in reliability have increasinglybecome stronger.

The multilayer ceramic capacitor normally produced by stacking aninternal electrode layer paste and a dielectric layer paste by a sheetmethod or a printing method, etc. and co-firing internal electrodelayers and dielectric layers.

As a conductive material of the internal electrode layers, Pd and a Pdalloy are generally used, but due to a high price of Pd, relativelyinexpensive base metals, such as Ni and a Ni alloy, have come to beused. When using a base metal as a conductive material of the internalelectrode layers, co-firing of the dielectric layers and the internalelectrode layers has to be performed in a reducing atmosphere becausefiring in the air results in oxidization of the internal electrodelayers. However, when firing in a reducing atmosphere, the dielectriclayers are reduced and the specific resistance is liable to decline.Therefore, a non-reducing dielectric material has been developed.

However, in multi-layer ceramic capacitors using a dielectric ceramiccomposition, IR (insulation resistance) remarkably deteriorates due toan electric field application, namely, there is a disadvantage that anIR lifetime is short and the reliability is low.

Also, a preferable temperature characteristic of a capacity is alsodemanded in a capacitor and, particularly, the temperaturecharacteristic of the capacity is demanded to be flat under a strictcondition depending on the use object. In recent years, multilayerceramic capacitors have come to be used in a variety of electronicdevices mounted in engine compartments of automobiles, such as anelectronic control unit (ECU), a crank angle sensor and an Anti LockBrake System (ABS) module. Since these electronic devices are for stableengine controlling, drive controlling and brake controlling, preferabletemperature stability of the circuit is required.

To overcome the disadvantages, for example, the Japanese PatentPublication No. 3348081 discloses a dielectric ceramic composition,wherein a containing ratio of rare earth oxides is made high comparingwith a conventional X7R-characteristic material and a content of anoxide of an element selected from Mg, Ca, Ba, Sr and Cr is 0.1 to 3moles. According to the invention described in the article, since easilyevaporating Pb, Bi and Zn are not included, firing in a reducingatmosphere becomes possible, so that it is possible to obtain adielectric ceramic composition, wherein a temperature characteristic ofthe capacity can be improved and the X8R characteristics are satisfied.

Also, the Japanese Patent Publication No. 3341003 discloses a dielectricceramic composition satisfying the X8R characteristics even if it ismade thin by decreasing a content of an oxide of an element selectedfrom Mg, Ca, Ba and Sr comparing with the dielectric ceramic compositionof the Japanese Patent Publication No. 3348081. According to theinvention described in the article, the X8R characteristics can beobtained without using an expensive lanthanoid among rare earth oxides.

However, although the temperature dependency of the capacity is improvedin the inventions described in the above articles, there is adisadvantage that the IR temperature dependency is large anddeterioration of resistance (IR) is particularly notable when used undera high temperature and the reliability becomes poor.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a highly reliableelectronic device, such as a multilayer ceramic capacitor, having low IRtemperature dependency and an excellent average lifetime characteristicand the production method.

To attain the above object, according to the present invention, there isprovided an electronic device having an element body, wherein dielectriclayers and internal electrode layers are alternately stacked, wherein:

a hetero phase is formed in the dielectric layers and/or the internalelectrode layers; and

the hetero phase includes a Mg element and a Mn element.

In the present invention, by forming a hetero phase including a Mgelement and a Mn element in the dielectric layers and/or the internalelectrode layers, deterioration of the IR at a high temperature can beeffectively prevented and the IR temperature dependency can be improved.Also, by forming the hetero phase, the average lifetime characteristiccan be improved and the reliability can be improved.

The “IR temperature dependency” is an index for accessing how theinsulation resistance IR changes due to temperature changes. The IRtemperature dependency can be evaluated by calculating a ratio (changerate) that IR at a predetermined temperature (for example, 150° C.) ischanged from IR at a reference temperature (for example, the roomtemperature of 25° C.). It is evaluated that the smaller the change rateof the IR between a plurality of temperatures, the more superior the IRtemperature dependency is; while, the larger, the poorer the IRtemperature dependency is. For example, even if a temperaturecharacteristic of the capacitance is satisfied, when the IR temperaturedependency is poor particularly under a high temperature, the practicaluse becomes difficult as a product.

In the present invention, when assuming that the room temperature (25°C.) and a high temperature part (150° C.) are used as examples of theplurality of temperatures and insulation resistance at the respectivetemperatures are IR₂₅ and IR₁₅₀, the IR temperature dependency isevaluated to be good or bad by calculating values of “a loss ofsignificant digits of IR” expressed by the formula (I) below. In the“loss of significant digits of IR”, the larger the value is (the smallerthe absolute value is), the lower the IR temperature dependency is. Inthe present invention, the “loss of significant digits of IR” expressedby the formula below can be made −2.00 or more.log(IR₁₅₀/IR₂₅)  (1)

In the present invention, preferably, the hetero phase is formed atleast at a part near boundaries of the dielectric layers and theinternal electrode layers.

By forming the hetero phase near boundaries of dielectric layers andinternal electrode layers, the IR temperature dependency can be moreeffectively reduced. Note that in the present invention, it ispreferable when the hetero phase is formed substantially near boundariesof the dielectric layers and internal electrode layers and, for example,it may be formed in the dielectric layers or in the internal electrodelayers.

In the present invention, preferably, the internal electrode layersinclude a Ni element as a main component. The Ni element may beincluded, for example, in a form of a Ni alloy, and alloys of one ormore kind of element selected from Mn, Cr and Co with Ni may bementioned as the Ni alloy. As a result that the Ni element is includedin the internal electrode layers, formation of the hetero phase becomeseasy.

In the present invention, preferably, the internal electrode layersinclude a cation element, wherein an effective ionic radius at the timeof 6 coordination is in a range of 0.065 to 0.085 nm, by more than 0 wt% and 2.4 wt % or less with respect to the entire internal electrodelayers. As the cation element, elements of I (0.067 nm), Ge (0.067 nm),Al (0.0675 nm), Cu (0.068 nm), Fe (0.069 nm), Ni (0.070 nm), Au (0.071nm), As (0.072 nm), Cr (0.0755 nm), Ga (0.076 nm), At (0.076 nm), Os(0.077 nm), Nb (0.078 nm), Ta (0.078 nm)m Co (0.079 nm), Rh (0.080 nm),Ir (0.082 nm), Ru (0.082 nm) and Sn (0.083 nm) may be mentioned, and anAl element is particularly preferable among them. Note that numbers inbrackets indicates an effective ionic radius at the time of 6coordination. Also, an ionic radius described in the presentspecification is a value based on the article “R. D. Shannon, ActaCrystallogr., A32, 751 (1976)”.

In the present invention, preferably, the internal electrode layersinclude a Mg element and/or a Mn element.

In the present invention, preferably, the hetero phase furthermoreincludes a Ni element.

In the present invention, preferably, the hetero phase has apredetermined thickness, and the thickness is preferably 1 μm orthinner, and more preferably 0.5 μm or thinner.

In the present invention, the dielectric layer is preferably composed ofa dielectric material, such as calcium titanate, strontium titanate, andbarium titanate. Also, the dielectric layer may include a Mg element anda Mn element or a cation element, wherein an effective ionic radius atthe time of 6 coordination is in a range of 0.065 to 0.085 nm.

In the present invention, preferably, a ratio (t1/t2) of a thickness(t1) of the dielectric layer and a thickness (t2) of the internalelectrode layer satisfies 1≦t1/t2≦8. When t1/t2<1, that is, when athickness (t1) of the dielectric layer is too thin, short-circuitingdefective rate tends to become high. Also, when t1/t2>8, that is, whenthe thickness (t1) of the dielectric layer is too thick, the heterophase is hard to be formed and it is liable that an effect of improvingthe IR temperature dependency cannot be obtained.

According to the present invention, there is provided a productionmethod of an electronic device having an element body, whereindielectric layers and internal electrode layers are alternately stacked,including the step of:

forming pre-fired internal electrode layers for composing the internalelectrode layers after firing by using an internal electrode paste;

wherein the internal electrode paste includes a Ni element and a cationelement, wherein an effective ionic radius at the time of 6 coordinationis in a range of 0.065 to 0.085 nm.

In the production method in the present invention, preferably, thecation element is an Al element.

In the production method of the present invention, preferably, theproduction method of the present invention furthermore includes the stepof forming green sheets for composing the dielectric layers after firingby using a green sheet paste;

wherein the green sheet paste includes a Mg element and a Mn element.

In the production method of the present invention, preferably, theproduction method of an electronic device of the present inventionincludes the steps of:

forming a green chip by alternately stacking the green sheets and thepre-fired internal electrode layers;

firing the green chip to obtain a sintered body; and

annealing the sintered body;

wherein an annealing temperature in the step of annealing is higher than800° C. but not higher than 1300° C.

Alternately, according to the present invention, there is provided aproduction method of an electronic device having an element body,wherein dielectric layers and internal electrode layers are alternatelystacked, including the step of:

forming pre-fired internal electrode layers for composing the internalelectrode layers after firing by using an internal electrode paste;

forming green sheets for composing the dielectric layers after firing byusing a green sheet paste;

forming a green chip by alternately stacking the green sheets and thepre-fired internal electrode layers;

firing the green chip to obtain a sintered body; and

annealing the sintered body;

wherein:

the green sheet paste includes a Mg element and a Mn element; and

an annealing temperature is 1200 to 1300° C. in the step of annealing.

In the production method of the present invention, preferably, theinternal electrode paste includes a Mg element and/or a Mn element.

In the production method of the present invention, preferably, a heterophase including a Mg element and a Mn element is formed in thedielectric layers and/or the internal electrode layers.

In the production method of the present invention, preferably, thehetero phase is formed at least at a part near boundaries of thedielectric layers and the internal electrode layers.

In the production method of the present invention, preferably, a ratio(t1/t2) of a thickness (t1) of the dielectric layer and a thickness (t2)of the internal electrode layer satisfies 1≦t1/t2≦8.

An electronic device according to the present invention is notparticularly limited, and a multilayer ceramic capacitor, piezoelectricdevice, chip inductor, chip varistor, chip thermistor, chip resistor,and other surface mounted chip electronic devices (SMD) may bementioned.

According to the present invention, by forming a hetero phase includinga Mg element and Mn element in dielectric layers and/or internalelectrode layers in an electronic device, such as a multilayer ceramiccapacitor, it is possible to provide a highly reliable multilayerceramic capacitor and other electronic device having low IR temperaturedependency and excellent average lifetime characteristic.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects and features of the present invention willbecome clearer from the following description of the preferredembodiments given with reference to the attached drawings, in which:

FIG. 1 is a sectional view of a multilayer ceramic capacitor accordingto an embodiment of the present invention;

FIG. 2 is a sectional view of a key part of a multilayer ceramiccapacitor according to an embodiment of the present invention;

FIG. 3A is a picture showing an element mapping result of a Mg elementin dielectric layers and internal electrode layers, FIG. 3B is a pictureshowing an element mapping result of a Mn element in dielectric layersand internal electrode layers, and FIG. 3C is a picture showing abackscattered electron image of dielectric layers and internal electrodelayers according to an example of the present invention; and

FIG. 4A is a picture showing an element mapping result of a Mg elementof in dielectric layers and internal electrode layers, FIG. 4B is apicture showing an element mapping result of a Mn element in dielectriclayers and internal electrode layers, and FIG. 4C is a picture showing abackscattered electron image of dielectric layers and internal electrodelayers according to a comparative example of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Multilayer Ceramic Capacitor 1

As shown in FIG. 1, a multilayer ceramic capacitor 1 according to anembodiment of the present invention comprises a capacitor element body10, wherein dielectric layers 2 and internal electrode layers 3 arealternately stacked. Both end portions of the capacitor element body 10are formed with a pair of external electrodes 4 respectively conductingto the internal electrode layers 3 arranged alternately in the elementbody 10. A shape of the capacitor element body 10 is not particularlylimited, but is normally rectangular parallelepiped. Also, the size isnot particularly limited and may be a suitable size in accordance withthe use object.

The internal electrode layers 3 are stacked, so that the respective endsurfaces are exposed alternately to surfaces of two facing end portionsof the capacitor element body 10. The pair of external electrodes 4 areformed on both end portions of the capacitor element body 10 andconnected to the exposed end surfaces of the alternately arrangedinternal electrode layers 3, so that a capacitor circuit is configured.

Dielectric Layer 2

The dielectric layers 2 are composed of a dielectric ceramiccomposition.

A material for composing the dielectric ceramic composition is notparticularly limited and a dielectric material, such as calciumtitanate, strontium titanate and barium titanate, may be used.Particularly, barium titanate (preferably, expressed by a compositionformula Ba_(m)TiO_(2+m), wherein “m” satisfies 0.995≦m≦1.010 and a ratioof Ba and Ti satisfies 0.995≦Ba/Ti≦1.010) may be preferably used amongthese dielectric materials. Also, the dielectric layers 2 may include avariety of additive subcomponents.

Internal Electrode Layer 3

A conductive material included in the internal electrode layers 3 is notparticularly limited, but it is preferable to use Ni or a Ni alloy,which is relatively inexpensive base metal. By forming the internalelectrode layers 3 by Ni or a Ni alloy, formation of a later explainedhetero phase 5 can be accelerated. As the Ni alloy, an alloy of one ormore kinds of elements selected from Mn, Cr and Co with Ni ispreferable, and a content of Ni in the alloy is preferably 95 wt % ormore. Note that the Ni or Ni alloy may contain various trace components,such as P, by not more than 0.1 wt % or so. A thickness of the internalelectrode layer 3 may be suitably determined in accordance with the useobject, etc., but normally it is preferably 0.1 to 3 μm, andparticularly 0.2 to 2.0 μm or so.

In the present embodiment, the internal electrode layer 3 includes acation element, wherein an effective ionic radius at the time of 6coordination is in a range of 0.065 to 0.085 nm, preferably by more than0 wt % and 2.4 wt % or less, and more preferably 0.1 wt % or more and2.0 wt % or less with respect to the entire internal electrode layer. Asthe cation element, elements of I, Ge, Al, Cu, Fe, Ni, Au, As, Cr, Ga,At, Os, Nb, Ta, Co, Rh, Ir, Ru and Sn may be mentioned, and an Alelement is particularly preferable among them.

Hetero Phase 5

In the present embodiment, a hetero phase 5 as a segregation phaseincluding at least a Mg element and a Mn element and having a differentcomposition ratio from those of the dielectric layer 2 and the internalelectrode layer 3 is formed in the dielectric layer 2 and/or theinternal electrode layer 3. It is sufficient if the hetero phase 5 isformed in any one of the dielectric layer 2 or the internal electrodelayer 3 but, as shown in FIG. 2, it is preferable to be formed at leastat a part near a boundary of the dielectric layer 2 and the internalelectrode layer 3.

By forming the hetero phase 5 including a Mg element and Mn element inthe dielectric layer 2 or the internal electrode layer 3, a decline ofthe IR at a high temperature can be effectively prevented and IRtemperature dependency can be reduced. Particularly, by forming thehetero phase 5 at least at a part near a boundary of the dielectriclayer 2 and the internal electrode layer 3, an effect of improving theIR temperature dependency can be enhanced.

A content of a Mg element in the hetero phase 5 is preferably 10 to 50wt % or so with respect to the entire hetero phase 5. Similarly, acontent of a Mn element is preferably 0.1 to 50 wt % or so with respectto the entire hetero phase 5. When the content of a Mg element is toosmall, it is liable that an effect of reducing IR temperature dependencyis hard to be obtained. Note that the Mg element and Mn element exist asoxides in the hetero phase 5.

A shape and size of the hetero phase 5 are not particularly limited, butit is preferable that the hetero phase 5 has a predetermined thickness,which is preferably 1 μm or thinner, and more preferably 0.5 μm orthinner. When the thickness is too thick, a paraelectric layer portionincreases and the permittivity tends to decline.

In the present embodiment, a ratio (t1/t2) of a thickness (t1) of thedielectric layer 2 and a thickness (t2) of the internal electrode layer3 is preferably 1≦t1/t2≦8, and more preferably 2≦t1/t2≦6. When t1/t2<1,that is, when a thickness (t1) of the dielectric layer 2 is too thin, adistance between adjacent internal electrode layers 3 becomes too shortand the short-circuiting defective rate tends to increase. On the otherhand, when t1/t2>8, that is, when the thickness (t1) of the dielectriclayer 2 is too thick, formation of the hetero phase 5 becomes difficultand it is liable that an effect of improving the IR temperaturedependency cannot be obtained. Note that thicknesses of the dielectriclayer 2 and the internal electrode layer 3 are not particularly limitedbut the thickness (t1) of the dielectric layer 2 is normally 3 to 7 μmor so, and the thickness (t2) of the internal electrode layer 3 isnormally 0.5 to 2 μm or so.

External Electrode 4

A conductive material included in the external electrode 4 is notparticularly limited, but inexpensive Ni, Cu and alloys of these may beused in the present invention. A thickness of the external electrode 4may be suitably determined in accordance with the use object, etc., butnormally 10 to 50 μm or so is preferable.

Production Method of Multilayer Ceramic Capacitor

A multilayer ceramic capacitor in the present embodiment is produced bypreparing a green chip by a normal printing method and sheet methodusing a paste, firing the same, then, printing or transferring externalelectrodes and firing in the same way as in a multilayer ceramiccapacitor of the related art. Below, the production method will beexplained specifically.

First, dielectric ceramic composition powder included in a green sheetpaste is prepared and made to be slurry to fabricate a green sheetpaste.

The green sheet paste may be organic slurry obtained by kneading thedielectric ceramic composition powder with an organic vehicle or waterbased slurry.

As the dielectric ceramic composition powder, the above oxides, mixturesthereof, and composite oxides may be used, and also it may be suitablyselected from a variety of compounds to be the above oxides, mixturesthereof, and compounds to be oxides or composite oxides by firing, suchas carbonate, oxalate, nitrate, hydroxide and organic metal compound,etc., and mixed for use. A content of each compound in the dielectricceramic composition powder may be determined, so that a composition ofthe above dielectric ceramic composition after firing is obtained. In astate before being made to be slurry, a particle diameter of thedielectric ceramic composition powder is normally 0.1 to 1 μm or so asthe average particle diameter.

In the present embodiment, it is preferable that the green sheet pastefurthermore includes a Mg element and Mn element for forming the heterophase 5. Adding quantities of the Mg element and Mn element are notparticularly limited and may be suitably adjusted in accordance with aratio of the dielectric layer 2 and the hetero phase 5 after firing. TheMg element and Mn element may be added as oxides or powder of a varietyof compounds to be oxides or composite oxides by being fired.

The organic vehicle is obtained by dissolving a binder in an organicsolvent. The binder to be used for the organic vehicle is notparticularly limited and may be suitably selected from a variety ofnormal binders, such as ethyl cellulose and polyvinyl butyral. Also, theorganic solvent to be used is not particularly limited and may besuitably selected from a variety of organic solvents, such as terpineol,butyl carbitol, acetone, and toluene, in accordance with a method to beused, such as a printing method and sheet method.

Also, when using a water based paste as a green sheet paste, a waterbased vehicle obtained by dissolving a water-soluble binder anddispersant, etc. in water is kneaded with a dielectric material. Thewater-soluble binder used for the water based vehicle is notparticularly limited and, for example, polyvinyl alcohol, cellulose andwater-soluble acrylic resin, etc. may be used.

The internal electrode layer paste is fabricated by kneading aconductive material formed by Ni or a Ni alloy or a variety of oxides,organic metal compounds, and resinates, etc., which become Ni or a Nialloy after firing, with the above organic vehicle.

The internal electrode paste furthermore includes a cation element,wherein an effective ionic radius at the time of 6 coordination is in arange of 0.065 to 0.085 nm. As the cation element, elements of I, Ge,Al, Cu, Fe, Ni, Au, As, Cr, Ga, At, Os, Nb, Ta, Co, Rh, Ir, Ru and Snmay be mentioned and an Al element is particularly preferable amongthem. An adding quantity of the cation element is preferably more than 0wt % and 2.4 wt % or less with respect to Ni and a Ni alloy as aconductive material.

In the present embodiment, as a result that a cation element, wherein aneffective ionic radius at the time of 6 coordination is in a range of0.065 to 0.085 nm, is included in the internal electrode paste, andinternal electrode layers before firing are formed and fired, formationof the hetero phase 5, particularly, formation of the hetero phase 5near boundaries of the dielectric layers 2 and the internal electrodelayers 3 can be accelerated, a reduction of the IR at a high temperaturecan be effectively prevented, and a reduction of the IR temperaturedependency becomes possible.

A reason thereof is not entirely clear, but the reason below can beconsidered.

Namely, it is considered that the cation element included in theinternal electrode layers before firing gives an effect of acceleratingformation of the hetero phase 5, furthermore, this kind of elements moveclose to boundaries of the dielectric layers 2 and the internalelectrode layers 3 by annealing and accelerate formation of the heterophase 5 near the boundaries.

Note that a cation element, wherein an effective ionic radius at thetime of 6 coordination is in a range of 0.065 to 0.085 nm, is liable tomove close to the boundaries of the dielectric layers 2 and the internalelectrode layers 3 by annealing, so that the content in the internalelectrode layers 3 after firing reduces to 1/10 to 1/100 or so comparingwith that in the internal electrodes before firing.

Also, the internal electrode paste may furthermore includes a Mg elementand Mn element for forming the hetero phase 5. As a result of includingthese elements in the internal electrode paste, formation of the heterophase 5 can be accelerated.

Note that the cation element, wherein an effective ionic radius at thetime of 6 coordination is in a range of 0.065 to 0.085 nm, and the Mgelement and Mn element may be added as powder of oxides or a variety ofcompounds, which become oxides and composite oxides by firing.

An external electrode paste may be fabricated in the same way as that inthe internal electrode paste explained above.

A content of an organic vehicle in the pastes explained above is notparticularly limited and may be a normal content, for example, thebinder is 1 to 5 wt % or so and the solvent is 10 to 50 wt % or so.Also, additives selected from a variety of dispersants, plasticizers,dielectrics and insulators, etc. may be included in each paste. A totalcontent thereof is preferably 10 wt % or less.

When using a printing method, the green sheet paste and the internalelectrode layer paste are stacked and printed on a substrate, such asPET, cut to be a predetermined shape and removed from the substrate toobtain a green chip.

When using a sheet method, the green sheet paste is used to form a greensheet, the internal electrode layer paste is printed thereon, then, theresults are stacked to obtain a green chip.

Before firing, binder removal processing is performed on the green chip.The binder removal processing may be suitably determined in accordancewith a kind of a conductive material in the internal electrode layerpaste, and when using Ni, a Ni alloy or other base metal as theconductive material, the oxygen partial pressure in the binder removalatmosphere is preferably 10⁻⁴⁵ to 10⁵ Pa. When the oxygen partialpressure is lower than the above range, the binder removal effectdeclines. While, when the oxygen partial pressure exceeds the aboverange, the internal electrode layer tends to be oxidized.

As other binder removal conditions, the temperature rising rate ispreferably 5 to 300° C./hour and more preferably 10 to 100° C./hour, theholding temperature is preferably 180 to 400° C. and more preferably 200to 350° C., and the temperature holding time is preferably 0.5 to 24hours and more preferably 2 to 20 hours. Also, the firing atmosphere ispreferably in the air or a reducing atmosphere, and a preferableatmosphere gas in the reducing atmosphere is, for example, a wet mixedgas of N₂ and H₂.

An atmosphere at firing the green chip may be suitably determined inaccordance with a kind of a conductive material in the internalelectrode layer paste, and when using Ni, a Ni alloy or other base metalas the conductive material, the oxygen partial pressure in the firingatmosphere is preferably 10⁻⁹ to 10⁻⁴ Pa. When the oxygen partialpressure is lower than the above range, a conductive material in theinternal electrode layer is abnormally sintered to be broken in somecases. While, when the oxygen partial pressure exceeds the above range,the internal electrode layer tends to be oxidized.

Also, the holding temperature at firing is preferably 1100 to 1400° C.,and more preferably 1200 to 1300° C. When the holding temperature islower than the above range, densification becomes insufficient, whilewhen exceeding the above range, breakings of electrodes due to abnormalsintering of the internal electrode layer, deterioration ofcapacity-temperature characteristics due to dispersion of the internalelectrode layer component, and a reduction of the dielectric ceramiccomposition are easily caused.

As other conditions of the firing, the temperature rising rate ispreferably 50 to 500° C./hour and more preferably 200 to 300° C./hour,the temperature holding time is preferably 0.5 to 8 hours and morepreferably 1 to 3 hours, and the cooling rate is preferably 50 to 500°C./hour and more preferably 200 to 300° C./hour. Also, the firingatmosphere is preferably a reducing atmosphere and a preferableatmosphere gas is a wet mixed gas of N₂ and H₂.

After the firing in a reducing atmosphere, annealing is performed on thecapacitor element body. In the present embodiment, an object of theannealing is to re-oxidize the dielectric layers and form the heterophase 5.

The holding temperature at the annealing (annealing temperature) ispreferably higher than 800° C. but not higher than 1300° C., and morepreferably 900° C. or hither but not higher than 1300° C. When theholding temperature is in the above ranges, the hetero phase 5 can beeffectively formed and the IR temperature dependency can be improved.When the holding temperature is 800° C. or lower, oxidization of thedielectric layers become insufficient, the IR becomes low, formation ofthe hetero phase 5 becomes insufficient, and the IR temperaturedependency deteriorates. On the other hand, when the holding temperatureexceeds 1300° C., not only the internal electrode layers are oxidized toreduce the capacity, but the internal electrode layers react with thedielectric base material, and deterioration of the capacity-temperaturecharacteristics, a decline of the IR and a decline of the IR lifetimeare easily caused.

As other annealing conditions, the temperature holding time ispreferably 1 to 20 hours and more preferably 2 to 10 hours, and thecooling rate is preferably 50 to 500° C./hour and more preferably 100 to300° C./hour. Also, an oxygen partial pressure in the annealingatmosphere is preferably 10⁻³ Pa or higher, and particularly preferably10⁻² to 10 Pa. When the oxygen partial pressure is lower than the aboverange, re-oxidization of the dielectric layers becomes difficult, whilewhen exceeds the above range, the internal electrode layers tend tooxidize. A preferable atmosphere gas of the annealing is, for example, awet N₂ gas, etc.

In the above binder removal processing, firing and annealing, forexample, a wetter, etc. may be used to wet the N₂ gas and mixed gas,etc. In this case, the water temperature is preferably 5 to 75° C. orso.

The binder removal processing, firing and annealing may be performedcontinuously or separately.

End surface polishing, for example, by barrel polishing or sand blast,etc. is performed on the capacitor element body obtained as above, andthe external electrode paste is printed or transferred thereon and firedto form external electrodes 4. A firing condition of the externalelectrode paste is preferably, for example, at 600 to 800° C. in a wetmixed gas of N₂ and H₂ for 10 minutes to 1 hour or so. A cover layer isformed by plating, etc. on the surfaces of the external electrodes 4 ifnecessary.

A multilayer ceramic capacitor of the present invention produced asabove is mounted on a print substrate, etc. by soldering, etc. and usedfor a variety of electronic apparatuses, etc.

An embodiment of the present invention was explained above, but thepresent invention is not limited to the above embodiment and may bevariously modified within the scope of the present invention.

For example, in the above embodiment, a cation element, wherein aneffective ionic radius at the time of 6 coordination is in a range of0.065 to 0.085 nm, was included in the internal electrode paste whenproducing the multilayer ceramic capacitor 1, but this kind of elementis not necessarily included. Note that, in this case, the holdingtemperature (annealing temperature) in the annealing step has to be 1200to 1300° C. to form the hetero phase 5 effectively.

EXAMPLES

Below, the present invention will be explained based on furthermoredetailed examples, but the present invention is not limited to theexamples.

Example 1

First, BaTiO₃ as a main component, V₂O₅, CaZrO₃, Y₂O₃, Yb₂O₃ and(Ba_(0.6) Ca_(0.4))SiO₃ as subcomponents were prepared, respectively.

Next, the prepared subcomponents were subjected to wet grinding by aball mill for 20 hours, preliminary firing at 900° C. for 4 hours in theair, then, wet grinding by a ball mill for 20 hours for disintegratingto obtain subcomponent additives. Then, the main component and thepreliminarily fired subcomponent additives were subjected to wetgrinding by a ball mill for 19 hours and dried to obtain a dielectricmaterial. Note that blending ratios in the dielectric layer material wasas below.

BaTiO₃: 100 moles

V₂O₅: 0.1 mole

CaZrO₃: 1.5 mole

Y₂O₃: 2.0 moles

Yb₂O₃: 1.5 mole

(Ba_(0.6) Ca_(0.4))SiO₃: 3.0 moles

Next, by using the obtained dielectric material, 100 parts by weight ofthe dielectric material, 0.9 mole of MgO, 0.3 mole of MnO (note thatcontents of MgO and MnO are with respect to 100 moles of BaTiO₃), 5.0parts by weight of an acrylic resin, 2.5 parts by weight of benzyl butylphthalate, 6.5 parts by weight of mineral spirit, 4.0 parts by weight ofacetone, 20.5 parts by weight of toluene and 41.5 parts by weight ofmethylethyl ketone were mixed by a ball mill to be a paste, so that agreen sheet paste was obtained.

Next, 44.6 parts by weight of Ni particles, 1.5 parts by weight of Al₂O₃as a co-material, 52 parts by weight of terpineol, 1.5 parts by weightof ethyl cellulose and 0.4 part by weight of benzotriazole were kneadedby triple rolls to be slurry, so that an internal electrode paste wasobtained. Al₂O₃ as a co-material was added to be 2.5 wt % with respectto the Ni particles. Note that, in the present example, as explainedlater, Al₂O₃ included in the internal electrode paste is diffused nearboundaries of dielectric layers and internal electrode layers duringfiring. Consequently, a content of Al₂O₃ to be actually included in theinternal electrode layer after firing becomes less than that included inthe internal electrode paste.

By using these pastes, a multilayer ceramic capacitor 1 shown in FIG. 1was produced as explained below.

First, by using the obtained green sheet paste, a green sheet was formedon a PET film. After printing the internal electrode paste thereon, thesheet was removed from the PET film. Next, the green sheets andprotective green sheets (not printed with the internal electrode paste)were stacked and bonded with pressure to obtain a green chip.

Note that, in the present example, thicknesses of the green sheet andinternal electrode layer before firing were respectively changed, sothat a ratio (t1/t2) of a thickness (t1) of a dielectric layer 2 and athickness (t2) of an internal electrode layer 3 after firing becamet1/t2=0.1 to 9 (refer to Table 1 and Table 2).

Next, the green chip was cut to be a predetermined size, and binderremoval processing, firing and annealing were performed under conditionsbelow, so that a multilayer ceramic fired body was obtained.

The binder removal processing condition was the temperature raising rateof 30° C./hour, the holding temperature of 260° C., the temperatureholding time of 8 hours, and the atmosphere of in the air. The firingcondition was the temperature raising rate of 200° C./hour, the holdingtemperature of 1245° C., the temperature holding time of 2 hours,cooling rate of 300° C./hour and the atmosphere of wet mixed gas ofN₂+H₂ (the oxygen partial pressure was 10⁻² Pa).

The annealing was performed under annealing temperatures (800 to 1300°C.) shown in Table 1 and Table 2. Other annealing condition was thetemperature raising rate of 200° C./hour, the temperature holding timeof 2 hours, the cooling rate of 300° C./hour and the atmosphere of wetN₂ gas (the oxygen partial pressure was 10⁻¹ Pa). Note that a wetter,wherein the water temperature was 5 to 75° C., was used to wet theatmosphere gas at the time of firing and annealing.

Next, after polishing end surfaces of the obtained multilayer ceramicfired body by sand-blast, In—Ga was applied as an external electrode, sothat samples of a multilayer ceramic capacitor shown in FIG. 1 wereobtained. In the present example, as shown in Table 1 and Table 2,samples, wherein a ratio (t1/t2) of a thickness (t1) of a dielectriclayer 2 and a thickness (t2) of an internal electrode layer 3 satisfiest1/t2=0.1 to 9 and annealing temperatures are 800 to 1300° C., wereobtained.

A size of obtained capacitor samples was 3.2 mm×1.6 mm×0.6 mm, thenumber of dielectric layers sandwiched by internal electrode layers was4, a thickness (t1) of a dielectric layer was 1 to 9 μm, and a thickness(t2) of an internal electrode layer was 1 μm or 10 μm.

Note that a measuring method of the dielectric layer thickness was tocut the obtained capacitor sample on a surface vertical with respect toan internal electrode and to take a SEM picture of the cut surface.Then, a vertical line with respect to the internal electrode was drawnon the SEM picture and a distance from the internal electrode to anadjacent internal electrode facing thereto was measured. The measurementwas performed for 20 times, an average of the measurement values wasobtained, and the average value was considered as the dielectric layerthickness.

On each of the obtained capacitor samples, existence of a hetero phasewas confirmed by an EPMA analysis and measurement of a backscatteredelectron image (BEI), and IR temperature dependency (loss of significantdigits) was evaluated. Also, an average lifetime was measured onspecific samples.

EPMA Analysis and Measurement of Backscattered Electron Image (BEI).

On each of the capacitor samples, an EPMA analysis and measurement of abackscattered electron image (BEI) by a SEM were made.

In the EPMA analysis, a cut surface of dielectric layers and internalelectrode layers of each sample was subjected to EPMA measurement, andelement mapping of the Mg element and Mn element was performed. Themeasurement was made on a range of a scope of 30 μm×30 μm. Then,existence of a hetero phase including the Mg element and Mn element wasconfirmed from pictures obtained by the element mapping. Existence of ahetero phase in each sample is shown in Table 1. Also, pictures obtainedby the element mapping are shown in FIG. 3A, FIG. 3B, FIG. 4A and FIG.4B. Note that FIG. 3A and FIG. 3B are pictures of samples (samples ofexamples of the present invention), wherein t1/t2=3 and an annealingtemperature is 1300° C., and FIG. 4A and FIG. 4B are pictures of samples(samples of comparative examples of the present invention), whereint1/t2=3 and an annealing temperature is 800° C.

Measurement of a backscattered electron image (BEI) was made by taking aSEM picture of a cut surface of the dielectric layers and internalelectrode layers of each sample by using a scanning electron microscope(SEM: production number JSM-T300 made by JEOL Ltd.). The measurement wasmade on the same scope as that in the EPMA analysis. Pictures obtainedby the measurement are shown in FIG. 3C and FIG. 4C. Note that FIG. 3Cwas a picture of a sample (a sample of an example of the presentinvention), wherein t1/t2=3 and an annealing temperature was 1300° C.,and FIG. 4C was a picture of a sample (a sample of a comparative exampleof the present invention), wherein t1/t2=3 and an annealing temperaturewas 800° C.

IR Temperature Dependency (Loss of Significant Digits)

First, on each capacitor sample, insulation resistance IR₂₅ at 25° C.and insulation resistance IR₁₅₀ at 150° C. were measured, respectively.Measurement of insulation resistance (the unit is Q) was made afterapplying a DC 7V/μm for 60 seconds at 25° C. and 150° C. by using aninsulation-resistance tester (R8340A made by Advantest Corporation).Next, a loss of significant digits expressed by the formula (I) belowwas calculated from the insulation resistance values IR₁₅₀ and IR₂₅. Inthe present example, −2.00 or larger were considered preferable. Theresults are shown in Table 2.log(IR₁₅₀/IR₂₅)  (1)

Measurement of Average Lifetime

An average lifetime was measured respectively on capacitor samples,wherein t1/t2=3 and an annealing temperature was 800° C., 1000° C. and1300° C., and capacitor samples, wherein t1/t2=8 and an annealingtemperature was 1300° C., kept to be a state of being applied with adirect current voltage of 10 V/μm at 200° C. The measurement was made on10 capacitor samples, and an evaluation was made by obtaining an averagelifetime. In the present example, time from starting the applicationuntil the insulation resistance reduces by one digit was defined as alifetime. The longer the lifetime is, the more preferable. In thepresent example, 10 hours or longer was considered preferable. Theresults are shown in Table 3.

TABLE 1 Dielectric Internal Layer Electrode Thickness Existence ofHetero Phase Thickness Layer Thickness Ratio Annealing Temperature (t1)[μm] (t2) [μm] (t1/t2) 800° C. 900° C. 1000° C. 1100° C. 1200° C. 1300°C. 9 1 9 none none none none none none 8 1 8 none presence presencepresence presence presence 7 1 7 none presence presence presencepresence presence 5 1 5 none presence presence presence presencepresence 3 1 3 none presence presence presence presence presence 1 1 1none presence presence presence presence presence 1 10 0.1 none presencepresence presence presence presence

TABLE 2 Dielectric Internal Layer Electrode Thickness IR TemperatureDependency Thickness Layer Thickness Ratio Annealing Temperature (t1)[μm] (t2) [μm] (t1/t2) 800° C. 900° C. 1000° C. 1100° C. 1200° C. 1300°C. 9 1 9 −2.55 −2.34 −2.21 −2.14 −2.05 −2.01 8 1 8 −2.45 −1.99 −1.99−1.97 −1.8 −1.73 7 1 7 −2.34 −1.96 −1.95 −1.92 −1.76 −1.71 5 1 5 −2.14−1.96 −1.93 −1.89 −1.72 −1.65 3 1 3 −2.13 −1.93 −1.86 −1.79 −1.69 −1.621 1 1 −2.01 −1.86 −1.78 −1.71 −1.54 −1.49 1 10 0.1 — — — — — — Note that“—” in Table indicates short-circuiting.

Evaluation 1

Table 1 shows existence of a hetero phase including a Mg element and Mnelement in respective samples, wherein a ratio (t1/t2) of a thickness(t1) of a dielectric layer 2 and a thickness (t2) of an internalelectrode layer 3 after firing is 0.1 to 9 and an annealing temperatureis 800 to 1300° C., and Table 2 shows values of IR temperaturedependency (loss of significant digits) of the respective examples.

From Table 1, it was confirmed that a hetero phase including a Mgelement and Mn element was formed in the dielectric layers or internalelectrode layers in samples, wherein t1/t2=0.1 to 8 and an annealingtemperature was 900 to 1300° C.

From the picture (FIG. 3A) showing a result of mapping a Mg element of asample (sample of an example of the present invention), wherein t1/t2=3and an annealing temperature is 1300° C., the picture (FIG. 3B) showinga result of mapping a Mn element and the backscattered electron image(FIG. 3C), it is confirmed that a hetero phase including the Mg elementand Mn element is formed near boundaries of dielectric layers andinternal electrode layers. This tendency was also observed in othersamples, wherein a hetero phase including a Mg element and Mn element isformed. Note that FIG. 3A to FIG. 3C are pictures on the same scope,wherein white parts in FIG. 3A and FIG. 3B show segregation of the Mgelement and Mn element, respectively, and black parts in FIG. 3C showsNi electrodes.

On the other hand, in samples with an annealing temperature of 800° C.,it is confirmed that a hetero phase including a Mg element and Mnelement is not formed as shown in FIG. 4A to FIG. 4C, being differentfrom the samples with an annealing temperature of 1300° C. Note that,also in FIG. 4A to FIG. 4C, white parts in FIG. 4A and FIG. 4B showsegregation of the Mg element and Mn element, respectively, and blackparts in FIG. 4C shows Ni electrodes.

Also, from Table 2, all of samples, wherein t1/t2=1 to 8 and anannealing temperature was 900 to 1300° C., had a value of IR temperaturedependency (loss of significant digits) of −2.00 or larger, and IRtemperature dependency was confirmed to be low.

On the other hand, all of samples wherein t1/t2=0.1 had too thindielectric layers and resulted in short-circuiting defects. While, insamples wherein t1/t2=9, a hetero phase including a Mg element and Mnelement is not formed and the value of IR temperature dependency (lossof significant digits) was smaller than −2.00, which was poor.

Furthermore, in samples with an annealing temperature of 800° C., ahetero phase including a Mg element and Mn element is not formedregardless of the t1/t2 value, and the value of the IR temperaturedependency (loss of significant digits) was smaller than −2.00, whichwas poor.

From the above results, it was confirmed that a reduction of IRtemperature dependency was possible by forming a hetero phase includinga Mg element and Mn element. Furthermore, to form the hetero phaseincluding a Mg element and Mn element, it was confirmed that the ratio(t1/t2) of a thickness (t1) of the dielectric layer 2 and a thickness(t2) of the internal electrode layer 3 was preferably 1 to 8 and anannealing temperature was preferably 900 to 1300° C.

TABLE 3 Internal Dielectric Electrode Hetero Layer Layer ThicknessAnnealing IR Average Existence Phase Sample Thickness Thickness RatioTemperature Temperature Lifetime of Hetero Forming No. (t1) [μm] (t2)[μm] (t1/t2) [° C.] Dependency [h] Phase Rate (%) 3-1 Comparative 3 1 3 800 −2.13  5 none  0 Example 3-2 Example 3 1 3 1000 −1.86  20 presense10 3-3 Example 3 1 3 1300 −1.62  56 presense 17 3-4 Example 8 1 8 1300−1.73 241 presense 25

Evaluation 2

Table 3 shows IR temperature dependency, an average lifetime and aformation amount of a hetero phase of each of capacitor samples, whereint1/t2=3 and annealing temperatures were 800, 1000 and 1300° C., andsamples, wherein t1/t2=8 and an annealing temperature was 1300° C.Sample numbers 3-1 to 3-4 were given to the respective samples as shownin Table 3.

Note that the hetero phase forming rate was measured by the methodbelow.

First, each capacitor sample was cut on vertical surfaces with respectto the dielectric layers at three parts. Next, the cut surface wasobserved by enlarging it by magnification of 5000 times by a scanningelectron microscope (SEM) and, from the SEM image, a ratio of a heterophase (segregation phase) segregating near Ni electrodes was obtained byconverting to an area ratio. In the present example, it was assumed thata state where a hetero phase completely covers the Ni electrodes wasdefined to be the hetero phase forming rate of 100%, and a state wherethe Ni electrodes are not covered at all was defined to be the heterophase forming rate of 0%. Namely, it means that the higher the heterophase forming rate is, the larger the hetero phase amount segregatingnear the electrodes.

From Table 3, in the sample number 3-2, wherein t1/t2=3 and an annealingtemperature was 1000° C., the sample number 3-3, wherein t1/t2=3 and anannealing temperature was 1300° C., and in the sample number 3-4,wherein t1/t2=8 and an annealing temperature was 1300° C., a heterophase including a Mg element and Mn element was formed and the IRtemperature dependency and average lifetime were preferable.Particularly, by comparing the sample number 3-2 with the sample number3-3, it is confirmed that the IR temperature dependency and the averagelifetime can be improved by heightening the annealing temperature. Notethat when the annealing temperature exceeds 1300° C., it is liable thatthe internal electrodes are oxidized, so that the annealing temperaturehas to be not higher than 1300° C. Furthermore, by comparing the samplenumber 3-3 with the sample number 3-4, it is confirmed that the largerthe t1/t2 value becomes, the longer the average lifetime tends to be;and the smaller the t1/t2 value becomes, the more the IR temperaturedependency tends to improve.

On the other hand, in the sample number 3-1, wherein t1/t2=3 and anannealing temperature was 800° C., a hetero phase including a Mg elementand Mn element is not formed, and a value of the IR temperaturedependency (loss of significant digits) became smaller than −2.00, whichwas poor. Furthermore, the sample number 3-1 exhibited an averagelifetime of 5 hours, which was poor.

From the above results, it was confirmed that the average lifetimecharacteristic could be improved by forming a hetero phase including aMg element and Mn element.

Example 2

Other than using as the internal electrode paste pastes obtained byadding Al₂O₃ as a co-material respectively by 0 wt %, 2.5 wt %, 5 wt %,10 wt % and 20 wt % to Ni particles, samples of the multilayer ceramiccapacitor shown in FIG. 1 were produced in the same way as in theexample 1. Not that, in the present example, green sheets and internalelectrode layers before firing were formed, so that the ratio (t1/t2) ofa thickness (t1) of the dielectric layer 2 and a thickness (t2) of theinternal electrode layer 3 became 3, and an annealing temperature was1000° C.

On each of the obtained samples, an EPMA analysis and measurement of abackscattered electron image (BEI) by a SEM were made in the same way asthose in the example 1 so as to confirm an existence of a hetero phaseincluding a Mg element and Mn element and to evaluate IR temperaturedependency (loss of significant digits). Furthermore, in the presentexample, a line analysis from an upper end to a lower end of a Nielectrode was made by using a transmission electron microscope to obtaina content of an Al co-material (a residual quantity of the Alco-material) in the internal electrode layer after firing, and anaverage value thereof was considered as a content of the Al co-material.

TABLE 4 Internal Dielectric Electrode Al Co-material Al Co-materialLayer Layer Thickness Annealing Adding Residual IR Average SampleThickness Thickness Ratio Temperature Quantity Quantity TemperatureLifetime No. (t1) [μm] (t2) [μm] (t1/t2) [° C.] [wt %] [wt %] Dependency[h] 4-1 Example 3 1 3 1000 0 0 −1.96 20 4-2 Example 3 1 3 1000 2.5 0.2−1.86 21 4-3 Example 3 1 3 1000 5 0.4 −1.71 23 4-4 Example 3 1 3 1000 101.2 −1.61 26 4-5 Example 3 1 3 1000 20 2.4 −1.49 31

Evaluation 3

Table 4 shows results of an Al co-material adding quantity to theinternal electrode paste, an Al co-material residual quantity in theinternal electrode after firing, IR temperature dependency and anaverage lifetime. Table 4 also shows results of measurement on samplesnot added with the Al co-material. Sample numbers 4-1 to 4-5 were givento the respective samples as shown in Table 4.

From Table 4, when a content of the Al co-material in the internalelectrode paste increases, it is confirmed that the IR temperaturedependency (loss of significant digits) and the average lifetime tend toimprove and, particularly, an effect of improving the IR temperaturedependency is enhanced. Note that the reason why the IR temperaturedependency and the average lifetime were improved as a result that an Alco-material was included in the internal electrode paste was consideredbecause the Al co-material moved close to boundaries of dielectriclayers and internal electrode layers by annealing and formation of ahetero phase including a Mg element and Mn element became easier nearthe boundaries. Note that the reason why a quantity of the Alco-material remained in the internal electrode layer after firing isreduced comparing with the Al co-material quantity included in theinternal electrode paste was considered because the Al co-material movedclose to boundaries of the dielectric layers and internal electrodelayers.

From the above results, as a result that a cation element, wherein aneffective ionic radius at the time of 6 coordination was in a range of0.065 to 0.085 nm, was included in the internal electrode layers beforefiring, it was confirmed that a hetero phase including a Mg element andMn element could be more effectively formed, and the IR temperaturedependency and the average lifetime could be improved.

1. A production method of an electronic device having an element body, wherein dielectric layers and internal electrode layers are alternately stacked, including the steps of: forming pre-fired internal electrode layers for composing said internal electrode layers after firing by using an internal electrode paste; forming green sheets for composing said dielectric layers after firing by using a green sheet paste; forming a green chip by alternately stacking said green sheets and said pre-fired internal electrode layers; firing said green chip to obtain a sintered body; and annealing said sintered body; wherein said green sheet paste includes a Mg element and a Mn element, said internal electrode paste includes a Ni element and Al₂O₃ as a co-material, wherein the amount of Al₂O₃ is 5-20% by weight per 100% by weight of the Ni element, an annealing temperature in said annealing step is higher than 800° C. but not higher than 1300° C., each internal electrode layer includes the Ni element as a major ingredient and an Al element of not less than 0.4% by weight but not higher than 2.4% by weight with respect to the entire internal electrode layer, and a hetero phase including a Mg element and a Mn element is formed in said dielectric layers and/or said internal electrode layers.
 2. The production method of an electronic device as set forth in claim 1, wherein said hetero phase is formed at least at a part of boundaries of said dielectric layers and said internal electrode layers.
 3. The production method of an electronic device as set forth in claim 1, wherein a ratio (t1/t2) of a thickness (t1) of said dielectric layer and a thickness (t2) of said internal electrode layer satisfies 1≦t1/t2≦8. 